For the treatment of the disorder known as pulpitis, the diseased pulpa is removed mechanically from the root canal, and the root canal is cleaned and drilled out, filled with an elastic-plastic element or with a different filling material and then sealed. For the prior art, see, for example, Friedman et al. In J. Dent. Res., 54 (1975) 921-925, Briseno in Philipp J., 2, 90, 65-73 and U.S. Pat. No. 4,632,977. As root canal filling materials Briseno describes inter alia semi-rigid cements based on synthetic resin, zinc oxide eugenol, calcium hydroxide or glass ionomer. U.S. Pat. No. 4,632,977 proposed trans-polyisoprene-based filling materials, for example based on gutta-percha or balata. Gutta-percha points are commercially available, the standard composition thereof being 20% by weight of gutta-percha as matrix, from 60 to 75% by weight of zinc oxide as filler, from 1 to 17% by weight of heavy metal sulphates as X-ray contrast agent and from 3 to 4% by weight of waxes and resins as softener. This filling material is inert in the root canal and accordingly does not react with body tissue.
The determination of the exact working length in a root canal is one of the most important working steps of the endodontological treatment in the treatment of pulpitis and is crucial in terms of success or failure. The preparation of a tooth should end just before the apex, namely in the apical constriction, that is to say the narrowest portion of the root canal. If the root canals are not prepared to a sufficient depth and if the gutta-percha points used to seal the root canal are not pushed far enough into the root canal, bacteria may multiply in the remainder of the root canal, which will cause the patient problems. If the gutta-percha points are pushed beyond the root canal into the periapical tissue, pain and inflammation may occur.
Hitherto it has been customary to determine the apex by means of X-ray images, in practice with measuring files being introduced into the root canal. It transpired, however, that the radiological apex differs considerably from the anatomical apex: the anatomical apex is the point of the tooth that, morphologically, lies furthest from the chewing surface of the tooth; the radiological apex, however, is the point lying (geometrically) furthest from the chewing surface. As a consequence, incorrect determination of the length of the root canal occurred frequently, resulting in the problems described above. Moreover, it was often necessary to take several X-ray images per root canal, since the canal lengths can change when canal curvatures are straightened out, which necessitated considerable effort and resulted in the patient being subjected to a considerable radiation dose.
As a consequence, measurements of impedances were therefore carried out: a root canal instrument is connected to an endometry apparatus; current is supplied to the root canal via the root canal instrument, a hand or lip electrode being used as counter-electrode. When the resistance between the measuring electrode and the counter-electrode reaches a specific value, the tip of the instrument has reached the apex.
According to a further method of the prior art, gutta-percha points are coated with a conductive layer, for example, by dipping or vapor deposition, then inserted into the root canal and the impedance is measured. Gutta-percha points treated in that manner cannot, however, be joined to one another even by heating. Moreover, the silver used for the coating becomes corroded, which may result in problems given the large surface of the coating.
The goal of the present invention is accordingly to provide a root canal filling means that overcomes the mentioned disadvantages of the prior art. In particular, the position of the filling material in a root canal is to be able to be determined precisely, the material is then ideally to be able to remain in the canal and the canal is to be able to be filled in the customary manner.